Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D1/00—Coating compositions, e.g. paints, varnishes or lacquers, based on inorganic substances
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
  • C09D183/04—Polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C26/00—Coating not provided for in groups C23C2/00 - C23C24/00
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
  • C30B11/002—Crucibles or containers for supporting the melt
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
  • C30B15/10—Crucibles or containers for supporting the melt
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B35/00—Apparatus not otherwise provided for, specially adapted for the growth, production or after-treatment of single crystals or of a homogeneous polycrystalline material with defined structure
  • C30B35/002—Crucibles or containers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites

Definitions

• the present invention relates to a slip for producing a durable hard coating containing silicon nitride on a substrate, a shaped body comprising a substrate and a durable hard coating applied thereto which is abrasion- and scratch-resistant so that the shaped body is transportable, a process for producing such a shaped body and the use of such shaped bodies, in particular as melting crucibles for use in the field of corrosive nonferrous metal melts, in particular in the field of solar silicon processing, and also the use of such a shaped body as riser tube in aluminium metallurgy, in particular low-pressure aluminium casting.
• silicon bars comprising silicon particles, silicon granules or silicon pieces are carried out using crucibles made of graphite or silicon nitride, but mainly SiO 2 (fused silica). Silicon bars having the desired micro-structures and purities crystallize from the melt during precisely defined cooling processes, and these silicon bars are subsequently cut into thin wafers and form the active constituent of photovoltaic units.
• the solar silicon quality is not adversely affected by the materials used in processing, e.g. melting crucibles, and the silicon melt can solidify without defects and can be removed undamaged from the crucible.
• the materials used in processing e.g. melting crucibles
• adhesion, infiltration and diffusion lead to problems in the demoulding of the silicon bars, so that there is a risk of rupture or cracking of the polycrystalline silicon block.
• the corrosive silicon melt results in attack on the SiO 2 crucible, since a chemical reaction between Si and SiO 2 takes place to form volatile SiO. In addition, undesirable impurities from the crucible material get into the silicon melt in this way.
• adhering material on the solidifying or solidifying silicon block should be avoided at all costs, since silicon undergoes very large thermal expansions so that very small amounts of adhering material lead to mechanical stress and thus to fracture of the crystalline structure, which results in reject silicon material.
• riser tubes made of iron alloys or fused silica are used. Due to the highly corrosive aluminium melt at temperatures in the range from 650 to 800° C., these riser tubes have to be coated with refractory oxides or nitrides at regular intervals in order to avoid rapid dissolution of these materials in liquid aluminium. Use is here usually made of coatings of aluminium oxide or boron nitride which are applied from slips containing organic binders by dipping, brushing or spraying.
• the life of such coatings is limited to hours or a few days.
• riser tubes made of silicon nitride ceramic which are completely inert towards corrosive attack by aluminium melts, are also used as alternatives to the coated riser tubes made of iron alloy or quartz.
• the costs of these silicon nitride tubes are many times that of standard riser tubes with a coating.
• melts made of quartz, graphite or ceramic and provided with silicon nitride layers for the purpose of avoiding sticking between melting crucible and nonferrous metals after contact of the melting crucible with solidifying nonferrous metal melts, e.g. silicon melts, are known from EP 963 464 B1.
• the layers comprise a high-purity silicon nitride powder.
• the silicon nitride powders have a low oxygen content and a particular aspect ratio.
• These powder coatings are applied directly by the user before use of the melting crucibles and are produced by dispersing high-purity silicon nitride powder in a solvent and then applying it to the crucibles by, for example, spraying of the suspension.
• the solvent and any organic binder constituents used have to be removed by thermal after-treatment.
• the high-purity silicon nitride itself has been found to be very chemically resistant towards silicon melts.
• the weight of the melt alone leads to forced wetting or infiltration of the porous silicon nitride powder layer. This therefore has to have such a thickness that it cannot be totally infiltrated and can therefore still serve as release or demoulding layer.
• such thick layers are in turn correspondingly soft and not particularly abrasion-resistant, so that particular care has to be taken when charging the crucibles, not to mention avoidance of long transport routes or the dispatch of ready-to-use coated crucibles.
• the conventional crucible coatings for use in the field of solar silicon thus have the disadvantage that the coatings have a low mechanical stability, since these consist only of silicon nitride powder so that coating always has to be carried out immediately before charging of the crucibles with the silicon powder, granules or pieces. Prior coating of the crucibles other than directly at the point of use is thus not possible. Furthermore, owing to the soft powder coatings, extreme care has to be taken when charging the crucibles with large pieces of material in order to avoid damage to the layer. In addition, undesirable caked residues occur on demoulding because of infiltration of the porous silicon nitride powder layer by the molten silicon.
• DE 103 26 815 A1 describes a substrate having an anti-adhesive coating which is obtainable by applying a coating composition to a substrate and hardening, with the coating composition comprising a) solid particles of a release agent with the exception of boron nitride and b) a binder comprising surface-modified nanosize solid particles.
• the release agent particles are selected from among graphite, graphite compounds, metal sulphides, metal selenides and metal tellurides.
• the invention accordingly provides a slip for producing a durable hard coating on a substrate, comprising a) silicon nitride particles and b) a binder comprising nanosize solid particles and/or precursors of nanosize solid particles from production via a sol-gel process.
• the invention further provides a shaped body comprising a substrate having a durable hard coating, wherein the hard coating has been produced from an inventive slip as defined above.
• the invention further provides for the use of a shaped body according to the invention in the field of corrosive nonferrous metal melts, in particular the use of a shaped body in the form of a melting crucible for producing silicon melts, and the use of a shaped body in the form of a riser tube in aluminium metallurgy, in particular low-pressure aluminium casting.
• the surprising effect displayed by the hard silicon nitride coatings of the invention is that the rigidly bound silicon nitride particles present here do not hinder demoulding of solidified nonferrous metal melts and at the same time do not have the disadvantages of the porous and loose silicon nitride powder layer structure during transport and charging of the shaped bodies provided with such hard coatings.
• SiO 2 -based binder systems known from DE 103 26 769 B3 and DE 103 26 815 A1 are suitable for producing durable hard silicon nitride coatings for the applications envisaged according to the invention, since he would have expected that the additional inorganic binders or nanosize solid particles would make demoulding of the solidified nonferrous metal melts more difficult and that impurities would be introduced into the solidified nonferrous metal melts, in particular solar silicon blocks, which is to be avoided at all costs.
• the hard silicon nitride layers of the invention have, in particular, the following advantages:
• the layers of the invention have the further advantage that, owing to their dense structure, the layers act as diffusion barriers for impurities because they prevent direct melt-substrate contact.
• the binder used according to the invention which comprises nanosize solid particles and/or precursors of nanosize solid particles from production via a sol-gel process, is known in principle from DE 103 26 815 A1. It has been found that the silicon nitride particles can be bound durably and in a thermally stable fashion to substrate surfaces by means of this binder.
• a nanoparticle-containing nano-composite in particular in the form of a sol, is used as binder.
• a nanocomposite or a nanocomposite sol comprises a mixture of nanosize solid particles and preferably inorganic or organically modified, inorganic polycondensates or precursors thereof produced by the sol-gel process.
• the binder composed of nanoparticles or nanocomposite is usually present as a sol or dispersion.
• the hardened layer it represents a matrix former. Due to this purely ceramic structure of the layer, a number of requirements are met. Apart from the high-temperature stability and the purity of the coating, adhesion of the layer to the substrate and mechanical stability are ensured as a result of the hardness and abrasion-resistance of the layer.
• the nanosize solid particles are preferably metal oxide particles or systems which are converted into nanosize metal oxide particles after hardening by high-temperature treatment.
• the nanosize solid particles are selected from among SiO 2 , TiO 2 , ZrO 2 , Al 2 O 3 , AlOOH, Y 2 O 3 , CeO 2 , SnO 2 , iron oxides and Ta 2 O 5 or among precursors of these nanosize solid particles which are converted by means of the sol-gel process into these solid particles, with SiO 2 particles and/or precursors of SiO 2 particles which are converted by means of the sol-gel process into nanosize SiO 2 particles being particularly preferred.
• nanocomposites which are preferred according to the invention and their production by the sol-gel process are known in the prior art, in particular from DE 103 26 815 A1.
• the nanosize solid particles are surface-modified with a surface-modifier having a molecular weight of less than 1500, in particular a surface modifier containing an anhydride group, acid amide group, amino group, SiOH group, hydrolysable radicals of silanes and/or a ⁇ -dicarbonyl group.
• silanes of the above formula (I) are likewise given in DE 103 26 815 A1.
• the coatings of the invention are produced from alcoholic SiO 2 -forming sols in which high-purity silicon nitride powders are dispersed. Since silicon nitride tends to undergo hydrolysis in the presence of water, water-based formulations should not be used; instead alcoholic SiO 2 -forming sols are preferred. Furthermore, the use of high-purity starting chemicals (silicon nitride powder, silanes, alcohols, etc.) is preferred since very high-purity layers which, in particular, meet the requirements of the solar industry are obtained in this way.
• the substrate appropriately comprises quartz, graphite, ceramic (including silicon nitride ceramic), SiO 2 (fused silica) or an iron alloy.
• the shaped body is a melting crucible having a substrate composed of quartz, graphite or ceramic which is suitable for the processing of corrosive nonferrous metal melts, in particular silicon melts.
• the shaped body is a riser tube having a substrate composed of SiO 2 (fused silica) or an iron alloy for aluminium metallurgy.
• the process for producing a shaped body according to the invention comprises at least the following steps:
• the substrate can in some cases be advantageous to treat the substrate with diluted or undiluted binder sols or their precursors or other primers before contacting.
• the solids content of the slips can be set by addition of solvent as a function of the chosen coating process.
• the final hardening can be preceded by one or more drying steps at room temperature or slightly elevated temperature, for example in a convection drying oven and/or by heating of the shaped bodies themselves.
• drying and/or subsequent hardening can be carried out in a protective gas atmosphere, for example in N 2 or Ar or under reduced pressure.
• the thermal hardening is carried out taking into account the heat sensitivity, preferably by heat treatment at temperatures above 50° C., preferably above 200° C. and particularly preferably above 300° C.
• the layers can also be baked at relatively high temperatures, preferably at temperatures of from 500 to 700° C., provided that the substrate is sufficiently stable at these temperatures.
• the layers can be produced as multiple layers.
• gradated layers in which the type and purity of the silicon nitride particles used can vary, for example from the bottom (substrate side) upwards (melt side), can be formed.
• silicon nitride grades which differ in respect of purity, particle size or particle morphology can be used within the layer structure.
• different binder contents can also be introduced into the gradated layers.
• These gradated layers can also be produced and arranged as multiple layers.
• the shaped bodies of the invention having the durable hard coatings are suitable for use in the field of corrosive nonferrous metal melts such as melts of aluminium, glass, silicon and the like.
• Shaped bodies in the form of melting crucibles are suitable, in particular, for producing silicon melts, for accommodating liquid silicon and for crystallization of liquid silicon to form silicon blocks.
• Shaped bodies in the form of riser tubes are suitable, in particular, for use in aluminium metallurgy, very particularly preferably in low-pressure aluminium casting.
• the solids content is set accordingly, for example to 60-70% by weight for application by means of spray gun.
• the suspension is applied to the cleaned, dust-free, dry crucible, if appropriate in a plurality of layers, so as to produce a homogeneous layer thickness of, for example, 500-800 ⁇ m. After drying, the coating is fired at about 1000-1100° C. before use as melt crucible.
• the silicon nitride powder coating obtained should be bubble-free and crack-free and also have no other defects.
• the silicon nitride layer produced in this way has only limited resistance to being touched and should be treated with corresponding care.
• Injury to the coating has to be avoided not only during charging with pieces of Si, but charging also has to be carried out so that slipping of pieces of Si is avoided during melting so that no defects in the powder layer are produced here either.
• a dispersion of 60% by weight of silicon nitride powder in ethanol (water-free) is produced.
• An equal amount of the binder (Ino® sil S-38, Inomat GmbH) is added to the ethanolic silicon nitride dispersion with stirring (converse order of addition also possible) to produce a sprayable suspension containing 30% by weight of silicon nitride.
• the suspension is applied by spraying, with a plurality of layers being applied “wet to wet” to give layer thicknesses up to about 40 ⁇ m. After “airing” at room temperature, the coating is dried in a drying oven and subsequently fired at 500° C. for 30 minutes.
• the coated crucible can now be used in the melting process.
• the defect-free Si ingot obtained can be demoulded without problems.
• a dispersion of 60% by weight of silicon nitride powder in ethanol (water-free) is produced.
• the binder (Ino® sil S-38, Inomat GmbH) is added to the ethanolic silicon nitride dispersion in a ratio of silicon nitride:binder of 2:1 with stirring to produce a suspension containing 40% by weight of silicon nitride.
• the higher-viscosity suspension is applied by dip coating, casting or brushing/rolling, with layer thicknesses up to about 100 ⁇ m being applied.
• the coating After “airing” at room temperature, the coating is dried in a drying oven and subsequently fired at 500° C. for 30 minutes.
• the coated crucible can now be used in the melting process.
• the defect-free Si ingot can subsequently be demoulded without problems.
• a suspension containing 30% by weight of silicon nitride powder is produced directly in the liquid, ethanolic binder.
• the silicon nitride powder is incorporated continuously into the binder (Ino® sil S-38, Inomat GmbH) with stirring. To homogenize the mixture, it is treated on a roll mill for a number of hours.
• the agglomerate-free 30% strength by weight silicon nitride suspension obtained in this way is applied by spraying, with a plurality of layers being applied “wet to wet” to give layer thicknesses of up to about 40 ⁇ m. After “airing” at room temperature, the coating is dried in a drying oven and subsequently fired at 500° C. for 30 minutes.
• the coated crucible can now be used in the melting process.
• the defect-free Si ingot can be demoulded without problems.
• a suspension containing 60% by weight of silicon nitride powder is produced directly in the liquid, ethanolic binder.
• the silicon nitride powder is incorporated continuously into the binder (Ino® sil S-38, Inomat GmbH) with stirring.
• the binder can also be incorporated a little at a time into the initially charged silicon nitride powder. To homogenize the mixture, it is treated on a roll mill for a number of hours.
• the agglomerate-free 60% strength by weight silicon nitride suspension obtained in this way is applied by brushing and rolling, with layer thicknesses up to about 100 ⁇ m being applied. After “airing” at room temperature, the coating is dried in a drying oven and subsequently fired at 500° C. for 30 minutes.
• the coated crucible can now be used in the melting process.
• the defect-free Si ingot can be demoulded without problems.
• the embodiments of the inventive silicon nitride coatings described in the examples differ from the reference coating according to the prior art in their lower layer thicknesses.
• functional, i.e. defect-free (bubble-free, crack-free) release layers are always produced. Due to the binder present, these layers have significantly higher adhesive strengths and scratch resistances than the standard silicon nitride powder coating.
• the thinner coating the layers are not damaged when charging or/and melting pieces of Si, so that contact between melt and crucible, which on solidification leads to adhesion and thus to spalling and cracks, is avoided.
• the inventive silicon nitride coatings described are distinguished by the solids content, the silicon nitride:binder ratio and the layer thicknesses and accordingly the viscosity of the suspension, which determines the application technique used for the suspension, and the defect-free layers which can be achieved: the higher the silicon nitride:binder ratio, the thicker the layers; the lower the silicon nitride:binder ratio, the harder/more scratch resistant.
• the optimal coating system can thus be selected (matching to suspension production, to coating process and to the respective melting process).

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• 2005
  • 2005-10-21 DE DE102005050593A patent/DE102005050593A1/de not_active Ceased
• 2006
  • 2006-09-20 EP EP06019707.6A patent/EP1780307B1/de not_active Not-in-force
  • 2006-09-22 TW TW095135107A patent/TWI367240B/zh not_active IP Right Cessation
  • 2006-10-18 US US11/582,449 patent/US8012252B2/en not_active Expired - Fee Related
  • 2006-10-20 KR KR1020060102508A patent/KR100800053B1/ko not_active IP Right Cessation
  • 2006-10-20 CN CNA2006101371019A patent/CN1955228A/zh active Pending
  • 2006-10-20 JP JP2006286150A patent/JP5209195B2/ja not_active Expired - Fee Related
  • 2006-10-23 NO NO20064799A patent/NO20064799L/no not_active Application Discontinuation

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